This invention relates to an improved process for dry-spinning polymer solutions to form filaments. More particularly, the process is directed to drawing a flow of heated, inert gas across the filaments emerging from a spinneret, and directing the flow downward into the hollow center of the filament bundle.
Dry-spinning is a well-established method for producing filaments from soluble polymers, and apparatus for dry-spinning is well known. In the usual dry-spinning techniques a hot polymer solution is extruded through spinneret orifices arranged in a series of concentric circles, and then the solvent is rapidly evaporated by introducing a sheath of hot inert gas, called aspiration gas, at the top of the spinning cell and directing it downward around the emerging filaments.
A process wherein a portion of the aspiration gas is removed upward through the center of the spinneret is disclosed by Wier in his U.S. Pat. No. 3,737,508. In Wier's center aspiration process a portion of the aspiration gas introduced in the conventional manner is drawn perpendicularly across the emerging filaments near the exit face of the spinneret by means of a vacuum applied to a conduit provided in the center of the spinning head. This will cause a fresh gas stream to contact the filaments immediately below the spinneret, enhancing solvent removal in a critical zone before a skin has set on the filament surfaces.
The present invention referred to generallly as amplified center flow will be used either to supplement or supplant the center aspiration process of Wier.